Mass detection devices, such as mass detection resonators, are widely used in many industries. For example, mass detection resonators are used to detect the thickness of thin films in deposition systems.
Mass detection resonators exploit a change in a vibratory mass of a resonator, which can be detected sensitively via a change in the resonance frequency. Specifically, the change in vibratory mass dM of the resonator is related to the shift in the resonance frequency dω as follows,
                                          d            ⁢                                                  ⁢            ω                    =                                                    -                                  ω                  o                                            ⁢              dM                                      2              ⁢                              M                eff                                                    ,                            (        1        )            wherein ωo represents resonance frequency and Meff represents an effective mass of the resonator. Equation 1 demonstrates that the sensitivity of mass detection (i.e., a larger dω) can be increased by lowering the effective mass Meff of the resonator and/or by increasing the resonance frequency ωo of the resonator. Typically, a smaller resonator has a higher resonant frequency.
Progress towards higher mass detection sensitivity has been accomplished, e.g., down to 10−18 grams (g), using micro-machined resonators produced by focused ion beam milling (FIB). However, further improvements have proven difficult because smaller and lighter resonators translate into higher electrical impedances (of the resonator), while larger bandwidths and more sensitivity are required to detect the motion.
Thus, techniques for effectively improving mass detection sensitivity would be desirable.